It was widely regarded as the most serious haze event on record — and could exceed those unprecedented levels.

“Conditions in Singapore and south-eastern Sumatra are tracking close to 1997,” Mr Robert Field, a Columbia University scientist based at Nasa’s Goddard Institute for Space Studies, was quoted as saying by the US science agency.

“If the forecasts for a longer dry season hold, this suggests 2015 will rank among the most severe events on record.”

Mr Herry Purnomo, a haze expert at the Indonesia-based Centre for International Forestry Research, agreed the situation was akin to 1997, describing the magnitude of this year’s fires as “horrendous”.

“I believe the impact of the fires this year will be as bad as 1997, in terms of the cost,” he told AFP.